Ziegler-Natta catalyst systems are well known for their capability to polymerize olefins. They in general consist of a support which mostly is magnesium based onto which titanium component has been added along with organic compound known as internal donor. This catalyst when combined with co-catalyst and/or external donor comprise of the complete Ziegler-Natta catalyst system.
The particle size and its distribution is very important aspect of Ziegler-Natta catalysts as it effects the properties of the final polymer and hence its processibility. Generally, polymers having uniform particle distribution and uniformity in the particle size is preferred as leads to better and easy processing of the polymer. Keeping this aspect in mind various methodologies are adopted either at precursor or catalyst preparation stage to attain uniform particle size and distribution.
Various methodologies based on the chemical aspect of the formation of active MgCl2 and on the incorporation of titanium and internal donor are followed. U.S. Pat. No. 4,220,554 describes using alcohol to dissolve MgCl2 and the solution is then added in excess of TiCl4 in the presence of internal donor at higher temperatures to allow precipitation of active MgCl2. U.S. Pat. Nos. 4,399,054 and 4,469,648 describes the methodology for low temperature melt quenching of the dissolved MgCl2 with alcohol at higher temperatures followed by dealcholation. EP1273595 describes the usage of emulsion stabilizer for controlling the particle size and shape. The catalyst is synthesized by reacting dialkylmagnesium with monohydric alcohol followed by dicarboxylic acid dihalide and chlorinated hydrocarbons in presence of viscoplex. After washing and isolation of this product, it is further treated with titanium compound for the formation of ZN catalyst which shows activity for propylene polymerization. U.S. Pat. No. 4,330,649 describes the in-situ formation of MgCl2 by the reaction of a precursor such as Mg(OR)2 with TiCl4 in the presence of internal donor and halogenated solvent. U.S. Pat. No. 4,784,983 describe another methodology for obtaining uniform particles by dissolving MgCl2 in organic epoxy and phosphorous compound and then adding TiCl4. Further an auxiliary precipitant which can be organic anhydride or acid or ether or ketone is added to form precipitate which is separated and treated with TiCl4 and inert diluents to obtain solid catalyst.
It is well known in the prior art that internal donor exerts a great deal of influence on the catalyst performance of the catalyst component for olefin polymerization. They generally satisfy the high industrial requirements for catalyst properties like high activity, high stereoregularity and high productivity but their role as control on particle size distribution is not known.